The present invention relates to a production machine for the simultaneous manufacture of continuous cigarette rods. U.S. Pat. No. 4,336,812 filed by the same Applicant, G.D. S.p.A., describes a production machine of the aforementioned type, designed to manufacture two continuous cigarette rods simultaneously by feeding two belts of shredded tobacco over the same number of continuously moving adjacent paper strips. The sides of the latter are then overlapped and stuck down to form two cigarette rods which are then cut into cigarettes. On the aforementioned production machine, each paper strip is supplied with tobacco by a suction conveyor belt which, in turn, is supplied by a feed unit. According to the aforementioned American Patent, the said feed unit comprises two up channels, or flues, arranged side by side in relation to the direction in which the said paper strips are fed. The said channels are also assembled with the bottom inlets over a common conveyor belt and aligned crosswise in relation to the direction in which the said conveyor travels.
Downstream from the said inlets, the said channels fork out so that the top ends pass under the said suction conveyor belts which are arranged parallel to each other.
The known production machine described is not, however, without its drawbacks: as the tobacco from the said conveyor is fed into each of the said two sloping channels, it is forced along routes of different curvature the different flow resistances of which make it difficult to ensure, as is necessary, that exactly the same amount of tobacco is fed into the channels at all times. This applies in particular to the larger, heavier tobacco shreds which are less affected by the said suction means and may, in the case of the channel with greater flow resistance, fall off the end of the said conveyor and fail to be fed into the channel.
What is more, unless substantial alterations are made, the structure of the known production machine described does not provide for accurate control of the said channel sections for correcting any difference in flow.